This invention relates to methods for spin forming initially cylindrical workpieces such as containers and like articles, and more particularly, initially cylindrical metal containers. Typically, the spin forming operation imparts to the container a noncylindrical (e.g. bottle-shaped) though radially symmetrical configuration along at least part of its length.
One specific though nonlimiting application of the invention is in the formation of bottle-shaped containers of aluminum or other metal.
Metal cans are well known and widely used for beverages. Present day beverage can bodies, whether one-piece xe2x80x9cdrawn and ironedxe2x80x9d bodies, or bodies open at both ends (with a separate closure member at the bottom as well as at the top), generally have simple upright cylindrical side walls. It is sometimes desired, for reasons of aesthetics, consumer appeal and/or product identification, to impart a different and more complex shape to the side wall of a metal beverage container, and in particular, to provide a metal container with the shape of a bottle rather than an ordinary cylindrical can shape. Conventional can-producing operations, however, do not achieve such configurations.
For these and other purposes, it would be advantageous to provide convenient and effective methods of forming initially cylindrical side walls of containers or other workpieces into bottle shapes or other complex shapes, free of the difficulties (such as wrinkling of the workpiece wall) that sometimes attend such forming procedures.
The present invention broadly contemplates the provision of a method of spin forming a hollow workpiece having an initially cylindrical side wall portion with an axis and at least one open end, comprising disposing, coaxially within the side wall portion, a mandrel tapering conically in one direction from a region of maximum radius at which the mandrel is in substantially 360xc2x0 contact with the side wall portion; disposing a plurality of rotatable spin-forming discs symmetrically externally around and in edgewise contact with the side wall portion at a location, along the axis, through which the mandrel extends, for pressing inwardly against the side wall portion at that location; and rotating the workpiece about the axis while unidirectionally translating the workpiece along the axis (relative to the forming discs) in the direction of taper of the mandrel, moving the forming discs radially symmetrically in maintained edgewise spin-forming contact with the cylindrical side wall portion at the aforesaid location to vary the radial distance of the discs from the axis, and translating the tapering mandrel along the axis relative to the forming discs and the workpiece to vary the radius of the tapering mandrel at the aforesaid location concomitantly with the varying radial distance of the discs from the axis.
Conveniently or preferably, the rotating step comprises positively rotating the workpiece about its axis, with rotation being transmitted by the workpiece to the mandrel and forming discs by frictional contact of the workpiece therewith. The translating step may comprise translating the workpiece along the axis in the aforesaid direction of taper, and independently translating the mandrel along the axis, while the discs are substantially stationary in position along the axis. Alternatively, the translating step may be performed by translating the forming discs along the axis in a direction opposite to the direction of mandrel taper, and independently translating the mandrel along the axis, while the workpiece is substantially stationary in position along the axis.
The workpiece may be a cylinder of initially uniform radius, open at both ends, or a preformed container having one closed end. Also, it may include a noncylindrical portion disposed in tandem relation to the cylindrical side wall portion, in which case the method of the invention is employed only to form the latter portion.
In particular embodiments, the workpiece is a metal container, and spin forming in accordance with the invention is performed to impart a bottle shape to the workpiece. However, the invention in its broadest aspects is not limited to forming bottle shapes or to containers, but may be applied to hollow formable cylindrical workpieces for other decorative and/or functional purposes.
For especially severe forming operations, where the amount of deformation would result in wrinkling of the side wall portion of the workpiece if performed by a single set of discs, the plurality of discs may include two or more sets of symmetrically disposed discs arranged in tandem along the axis.
Further features and advantages of the invention will be apparent from the detailed description hereinbelow set forth, together with the accompanying drawings.